The songbird brain is distinguished by a network of nuclei important for learned vocal control via auditory feedback and many of the neurons throughout this network respond vigorously to the auditory presentation (playback) of the bird's own song (BOS), but not to the playback of conspecific songs. The neural network mechanisms that generate these highly selective auditory responses are unknown, but identifying where they arise along the auditory pathway is important to understanding how auditory signals influence vocal learning and how auditory experience shapes neuronal response properties. This application seeks to identify the synaptic level at which song selectivity emerges and the integrative mechanisms underlying selectivity by focusing on Nucleus Interfacialis (NIf), a sensorimotor nucleus that is important to song patterning and that contains neurons that are BOS-selective. The exact nature of NIf's auditory inputs remains unclear, although there are at least three possible sources: caudal Hyperstriatum Ventrale (cHV), Field L, and Nucleus Ovoidalis. The hypotheses of this application concern where the auditory input to NIf arises and the synaptic nature of the auditory inputs to NIf.